Going the distance… at a snail’s pace
Posted onJanuary 8, 2026byMariel Terebiznik|Canada's New Noahs, News and Events
Since 1988, the Canada’s New Noah program has provided young conservation biologists in Canada the opportunity of a lifetime. Each year, WPC selects a dedicated biologist from applicants across Canada to undertake a 3-month course at the Durrell Conservation Academy in the U.K. followed by a 6-month internship on the islands of Mauritius and Madagascar in the Indian Ocean. This is an opportunity unlike any other for young Canadians to learn firsthand how the world’s most successful conservation recovery programs are managed and to bring this knowledge and experience back to improve Canada’s conservation capacity. Mariel Terebiznik is WPC’s 34th Canada’s New Noah and reports on her experiences and how she will apply them on return to Canada. The Canada’s New Noah Program is generously supported by the Alan & Patricia Koval Foundation.
As a biologist, one of the most haunting questions you can ask (or be asked) is How many are there? The struggle to quantify the size of a population of animals has dominated fields in biology and the practice of conservation. While definitive answers are elusive, for conservationists a lot rides on understanding the population size of species you are trying to save. It affects management plans, conservation action, and species IUCN ratings (e.g., Vulnerable, Threatened, Extinct). Without a clear understanding of ‘how many’, planning conservation action is like navigating uncharted waters, you may have your destination in mind, but you do not know the route to get there nor the dangers that lurk along the way.
So how do we go about answering this question of How many? We can draw on a variety of techniques from complicated theoretical models to intense field work, often with a combination of both to try and approximate an answer. In Mauritius, as part of a training conducted by the Durrell Conservation Training, I got to try out one of these techniques known as Distance Sampling with the help of one tipti (Mauritian Creole for small) endemic snail called Tropidophora fimbriata.
Two snails on a tree. Photo: M. Terebiznik.
T. fimbriata is a blink-and-you-miss-it snail no bigger than the nail on your pinkie finger. It is so unassuming, it even lacks a common name and an IUCN rating. In an island full of conservation stories, T. fimbriata is not among those grandiose tales of Mauritius Kestrels and Echo Parakeets, but it still has its own epic story to tell. Already extinct in the neighbouring Reunion Island, one of its last remaining strongholds is the Mauritian Island of Ile Aux Aigrettes (IAA). With the eradication of rats, the reintroduction of the Telfair’s skink predating on T. fimbriata’s invasive African Land snail competitor, and ecological restoration of the plant community all for other conservation goals, T. fimbriata on IAA have made quite a comeback – somewhat by accident. Now thanks to these conservation actions, trees all over the island are decorated with these small snails providing a perfect system to put Distance Sampling to work.
Conducting a Distance Survey is simple enough in theory. All you need to do is walk a straight line marked by string, called a transect. Every time you see your species of interest, you record the perpendicular distance from where you saw the individual to the transect line. Walk enough transect lines and record enough species’ sightings, and you can calculate your population size using Distance Sampling models.
For us on IAA, this meant everyone on the team walking 40 transect lines spread out across the island looking for our snails. Our field work took several days to complete and had me seeing snails where none existed. I started questioning whether or not I knew what a snail looked like and dreaming of them as soon as I closed my eyes at night. Snail madness aside, with our data collected, the next step to answer this foreboding question of ‘how many’ was to learn to use the program Distance to analyze the data.
As we reviewed our data and spoke about our experience searching for these snails, we realized that we must have inevitably missed some individuals along our transect lines, especially with such a cryptic species like T. fimbriata. Luckily, Distance Sampling models account for this by assuming that the probability of detecting your species is 100% directly on the transect line and then decreases with distance from the transect. Using statistical models that a program called Distance runs, we can use these assumptions along with other information like area of the island, time per transect survey, weather conditions, etc. to calculate the probability of detecting our species at different distances. Knowing the area of the island and length of the transects we walked, Distance was able to extrapolate these results to determine how many T. fimbriata are on IAA.
It may have been at a snail’s pace, but after several days in the field and behind the computer, we can now say that on our 26-hectare island of IAA there are approximately 11,425 T. fimbriata snails. These Distance Sampling values showcase the stronghold that IAA is for these small endemic snails. So if you ever find yourself in Mauritius and heading to visit IAA, keep your eyes peeled. Among the regenerated ebony forest, singing Mauritius Fodys, and wandering Aldabra Tortoises, are 11,425 tipti endemic snails waiting to be noticed. Just take it from me and do not try to count them all.
Mariel Terebiznik
34th Canada’s New Noah
Mariel has always had a deep relationship with nature and conservation, having grown up spending most of her time outdoors in parks. Pursuing this passion, Mariel studied in ecology and evolutionary biology at the University of Toronto, where she received both her Bachelors and Master of Science degrees. There, Mariel focused on being in the field as much as possible, travelling to Ecuador to work with lizards and spending an inordinate amount of time in Algonquin Provincial Park contributing to long-term monitoring projects. Mariel also co-founded and co-directs a grassroots organization called Field Research in Ecology and Evolution Diversified (FREED).
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